1. Field of the Invention
The present invention concerns a gradient coil/radio-frequency antenna unit for a magnetic resonance apparatus of the type having a radio-frequency (RF) antenna and a gradient coil unit to generate a gradient magnetic field in an examination region of the magnetic resonance apparatus. The invention furthermore concerns a magnetic resonance apparatus with such a unit.
2. Description of the Prior Art
Magnetic resonance technology is a known modality to, among other things, acquire images of the inside of a body of an examination subject. In a magnetic resonance apparatus (MR apparatus), rapidly switched magnetic gradient fields that are generated by gradient coils are superimposed on a static base magnetic field B0 that is generated by a basic field magnet. To trigger magnetic resonance signals, the magnetic resonance apparatus also has a radio-frequency antenna that radiates RF signals, known as the B1 field, into the examination subject. The triggered magnetic resonance signals can be acquired with this antenna or further local antennas and processed into magnetic resonance images.
For example, U.S. Pat. No. 6,433,550 discloses an open magnetic resonance apparatus with a C-shaped basic field magnet that has
For example, U.S. Pat. No. 6,433,550 discloses an open magnetic resonance apparatus with a C-shaped basic field magnet that has one pole plate at each of the two ends of the C-structure on both sides of a patient acceptance chamber arranged in the opening of the C-structure, between which the basic magnetic field of the magnetic resonance apparatus can be generated, at least within the patient acceptance chamber. Essentially planar parts of a gradient coil system, and likewise planar parts of an antenna system of the magnetic resonance apparatus connected to the gradient coil system, are also arranged at each of the pole plates facing the patient acceptance chamber. Gradient coils for the aforementioned gradient coil system are described in German OS 40 37 894 and German OS 44 22 781.
An antenna arrangement for a magnetic resonance apparatus in which a basic magnetic field is established between two pole plates is also known from German OS 42 32 884. A sub-antenna into which a radio-frequency current is fed is arranged at each pole plate. The sub-antennas are formed by a sealed, grounded shield facing the pole plate and a laminar conductor structure disposed at a distance from the shield and essentially parallel thereto.
Furthermore, from German OS 42 32 884 the desirability of keeping the pole plate separation optimally small so that the weight of the basic field magnets remains low and a better basic magnet field homogeneity is achieved. For this reason it is advantageous to keep all internal components between the pole flanges (such as the gradient coil system, the radio-frequency shield and the antenna arrangement) as flat as possible. This competes with the fact that an optimally large separation of the antenna arrangement from the radio-frequency shield is advantageous for a high degree of efficiency of the antenna arrangement. This is particularly true given the use of the antenna arrangement to receive magnetic resonance signals.
A circular, planar radio-frequency antenna for open magnetic resonance apparatuses is known from German OS 101 24 737. It has two separated systems made from planar conductors for currents arranged on a carrier plate. To tune to the desired resonance frequency, the conductors are capacitively shorted at least at one end by tuning capacitors connected to ground. Only one planar metal layer into which currents offset by 90°, are fed is arranged on each carrier plate. Tuning capacitors are arranged at the infeed location and the opposite side.
Since in general in magnetic resonance systems the space within the homogenous basic magnetic field B0 is costly and therefore scarce, every attempt to minimally occupy the available space by integration or maximum use of the available space for the patient is advantageous.